The present invention generally relates to a liquid jet recording head driving method, and more particularly to a method of driving a drop-on-demand ink jet printing head in which reliability is improved and the print quality is enhanced by means of a simple, low-cost driving circuit for applying a drive signal to the printing head.
There has been known a drop-on-demand ink jet printing head in which an electromechanical transducer is selectively energized to produce ink drops on demand. More specifically, in such a printing head, a drive signal is applied to a piezoelectric element so as to generate a pressure wave in ink within in ink cavity (or, a pressure chamber) by the energized piezoelectric element, and an ink droplet is discharged onto a recording member due to the pressure wave. In the printing head, an ink droplet is discharged via a nozzle at an end portion of the pressure chamber in accordance with the drive signal being applied, the drive signal representing a demand for discharging the ink. It is advantageous that the drive signal is applied to the printing head by means of a simple, low-cost driving circuit. Extensive efforts have been made to improve reliability and enhance the print quality and resolution of the drop-on-demand ink jet printing heads.
Japanese Patent Publication No. 2-24218 (corresponding to Japanese Laid-Open Patent Publication No. 57-59774) discloses a method of driving a drop-on-demand ink jet head. In this driving method, a transducer (a piezoelectric element) is energized by a low-voltage signal so as to achieve a desired ink discharge velocity. A prescribed voltage, being positive with respect to a polarized voltage of the transducer, is applied to charge the transducer so that the capacity of an ink passage in the head is decreased. When a pulse signal having a falling edge the voltage of which gradually falls from the applied voltage is applied to discharge the transducer, the capacity of the ink passage is increased. When a rising edge of the pulse signal the voltage of which sharply rises is then applied, the ink passage capacity is decreased and ink within the ink passage is discharged from a nozzle at an end of the ink passage. However, in this driving method, it is difficult to reduce the magnitude of natural oscillation (or, residual oscillation) of the transducer occurring due to the application of the pulse signal. Thus, a desired print quality of the ink jet printing head cannot be achieved.
Japanese Laid-Open Patent Publication No. 59-176060 discloses a method of driving an ink jet printing head. In this driving method, a drive signal is applied to the piezoelectric element so that ink within the pressure chamber is discharged. Generally, natural oscillation of the piezoelectric element occurs due to application of the drive signal. At least one supplementary signal having a phase different from the phase of the drive signal is subsequently applied so as to improve the repetition frequency characteristic. However, in this driving method, the phase difference between the drive signal and the supplementary signal is not appropriate for reducing the magnitude of the natural oscillation. In other words, a voltage falling edge of the supplementary signal is applied, so as to decrease the pressure of the ink, earlier than a time when the ink is completely discharged due to application of the drive signal. Therefore, it is difficult to reduce the magnitude of the natural oscillation sufficiently, the ink discharge velocity thus having undesired variations and a desired print quality cannot be achieved. In addition, the timing of application of the supplementary signal and the pulse duration thereof are not clearly defined with respect to the drive signal, and therefore the ink jet printing head driving method as mentioned above is not suitable for practical use.